Aircraft: MEDIUM TRANSPORT
Phase of flight: Taxi
Anomaly: Ground Event / Encounter Other / Unknown; Ground Excursion Taxiway

This event happened on the ramp at CYWG in the morning. It had been snowing throughout the night and morning and everything was covered with about 3' to 4' of snow. The airport operations was in the process of clearing the runways at the time of our arrival at the airport and had yet to begin working on clearing the taxiways and ramp areas. The preflight and boarding process went smoothly and without incident. As the First Officer (FO) and I were both familiar with the airport; neither of us had de-iced at CYWG and we spent most of our preflight briefing talking about where and how we would get to the deice pad. We noticed that there were a couple different routes we could take to get there. We decided that more than likely; as the ramp was going to be occupied with other aircraft pushing back; that the ground controllers would send us to the deice pad via taxiway K which was right behind our gate. After completing the Before start/push back checklist of the Deicing/Anti-Icing Configuration Checklists in the QRH; we begun the push back. The FO and I discussed that we should start both engines such that it would lower our workload; and that it would give the engines plenty of time to warm up given the outside air temp. During the pushback; we could see another aircraft that had pushed from the gate to our right; and we could hear their communications with the ground controller about some maintenance problem that they were having. The other aircraft's maintenance personnel had their trucks parked next to it such that the mechanic could stand on the roof of the truck and talk to the pilot via their window. The ramp agents disconnected the tow bar and quickly left to go inside; there was no wave off given. With the weather conditions as they were; I remember thinking that I didn't blame them for the obvious desire to go get warm. The engines started normally and we finished the After Start portion of the checklist. My thought process at this time was that since the ramp area was pretty big behind us; and since the other aircraft was off our right wing; that the only option to get to the deice pad was to use Taxiway K and that a left 180 degree turn would be our only option. The FO called the ground controller and asked for permission to taxi for deice. The instructions given to us were to taxi via K; F; W; and the apron to the deice pad. So; at this point all was going as we had briefed. We could see out our front windows clearly; however; our side windows were still covered in snow and ice which made for very poor visibility. However; my FO could see well enough through his side window to tell that his wing was clear; and I could see well enough to tell that no aircraft was to our left. I began to commence the left hand 180 to get to taxiway K. As we came around; at a very slow speed; it was very difficult to tell where any markings were; in fact we couldn't see any. We didn't quite make it to 180 degrees when my alert FO told me to stop. I straightened out the nose wheel; stopped; and put on the parking brake. I asked him if he could see taxiway K which he then informed me that he could only see a blue taxi light out his window and that he thought we had only grass ahead of us. I at first didn't believe that that could be true as I could see tire tracks in the snow in front of us. I opened my window to gain a better advantage and at that I point see another blue taxi light creeping up above the snow. My FO was right. As there was no 'bump' or any indication to us that we had driven off the concrete and onto the grass; we were thinking; and hoping that we were still on the pavement. While we were trying to figure out exactly where we were and what had gone wrong; the ground controller asked if we needed assistance. We said that we probably will as we believed we were facing the grass and not a taxiway. After asking if we needed assistance; ground controller asked another aircraft if they too needed assistance which I believe they declined. My FO tried calling ops several times without any luck. At this point I asked the ground controller if he had a phone number to our operations; which he said that he had alerted the airport field operations and that they were on their way. After about 45 minutes of waiting a ramp agent showed up with the airport field chief and informed us that we indeed had our nose wheel three feet past the concrete and on the grass. I was so surprised by this information. The ramp agent at this point called our dispatch; took pictures and left us for another 30 minutes. We made as many PA's as we thought were needed to keep the passengers informed; and our FA did a fantastic job of keeping them comfortable and calm. From this point; with the snow and weather as it was; we were told that buses would take hours to get to us. Our operations; with the cooperation from the airport and CBP; deplaned our passengers via airport operation pickup trucks. After the passengers were off the plane; the head ramp agent was able to push the empty aircraft off the grass and back to the gate without any problem at all. The push was done with minimal power from the tug; and was as normal push back from any gate. Just as before; there was no indication for us sitting on the AC during the push off the grass that we had changed surfaces. No bump; no drop off; it was as smooth as could be. From here we waited for mechanics to fly in to conduct an inspection. In retrospect what I believe happened and where I lost situational awareness was during the push back. I was paying attention to the engines start and to what was going on with the other aircraft. Turns out that the ramp personnel didn't push us straight back as I assumed they would do with our tail facing taxiway K; but rather they angled our tail slightly to the northeast. They also pushed us back further than I was expecting. This put our aircraft with our tail facing the corner of the apron and taxiway K and making my left 180 degree turn impossible to get to taxiway K. From the ramp agents' point of view; I can understand why they did this if they were thinking this action would make a right turn easier for us. However; no communication between the ramp agent pushing us back and us concerning this maneuver existed. So; since the visibility out my window was compromised; my paying attention to the engine starts and the other aircraft; my situational awareness suffered. I turned left; when I should have waited for the other aircraft to finish with their maintenance delay and turned right. There were many threats to this flight; with the weather being the biggest. The lack of visibility out our side windows is another. Also; as this was the first major snow storm for the area; the fact that there was the same amount of snow that covered the concrete and the grass left no visible distinction between the two. I still don't know why there were tire tracks through the grass area which made it look just like a taxiway. If it wasn't for the blue lights poking up through the snow in the dim morning light; we would have had no idea where the concrete ended and where the grass began. The fact that the apron and taxiways were not plowed was also another threat. The errors were mostly on my part for the lack of situational awareness as to where the push back had located our aircraft on the apron. Another error I made was the lack of communication with the agent pushing us back. I could have asked him (as he had a better view point of the apron area) if we could make the left turn. Had I done that; I believe he would have informed me that I couldn't and that a right hand turn was the only option. I have learned a lot from this experience. I have learned that good CRM is critical at every phase of flight. The FO and I; I believe; used proper CRM to handle this situation. The FO is a great communicator and is easy to work with. As soon as I heard him say 'STOP' I knew that he had seen something and that I needed to comply. We worked well together as a team throughout this situation. I also have learned that I need to keep a high level of situation awareness even when things are going as we had briefed. Just because things are happening as planned doesn't mean that it's ok to let your situational awareness drift. I simply turned left when I should have turned right; and had I maintained my situational awareness; communicated with the ramp agent; this wouldn't have happened. I also learned the importance of good visibility out our windows. I could have made a better effort to clear off the snow from the side window. However; given that most of it was ice; I know I couldn't have scrapped it off. I feel terrible for having made this mistake and will learn from it. I am grateful that during this incident no damage was caused to the aircraft; or airport facilities. I know that this is a side note and not important; but I have seen other airlines use iPads that show with GPS accuracy their exact location on the 10-9 page. That would have been great in this situation as it would have shown our exact location to taxiway K. We showed up to the airplane on time and completed our safety and receiving checks. During the walk around it was evident that we would need to deice since it was snowing; blowing snow and gusty winds with a temperature of approximately -16c with low visibility. We boarded the airplane and did our receiving checklist followed by the QRH deicing/anti-icing configuration checklists. We briefed our taxi route along with everything else and the Captain (CA) mentioned we would more than likely taxi out via K and that it was right behind us. He asked me if I was familiar with the airport and I had told him that I was. He also briefed that we would start both engines before moving. Our entire aircraft was covered in snow and our side windows were completely frozen over. Both the front windshields were clear. The ramp or apron was uncontrolled and once we were both ready we asked the tug driver to push us back. During the push we started engine #2 and discussed that it would take a while for the engines to warm up in this cold. Ground crew completed their push; disconnected and took off. I never saw a wave off. Sitting there we started engine #1 and completed the QRH after start checklist. While sitting there I called Ground and advised him that we were ready for taxi and needed to head over to the ice pad for deice. The instructions we received were taxi to ice pad via K; F; W; transition through the apron and call pad control on 122.92 short of the pad. During the push back we had seen another aircraft off to the right of our airplane. Since it was hard to see out our windows the CA said he was going turn left to join K since K is right behind us and made a remark about keeping clear of the other aircraft on my side. I remember glancing over to my 10-9B page because the apron and all taxiways were completely covered in 3 inches of snow and couldn't see the signs for K as we started to make the 180 degree left turn. When we completed the turn I kept looking for an indication of being on K since I thought it was directly behind us. The CA had just straightened out the nose wheel and had started to move slightly forward when I saw a blue taxi light out my window. I still could not see any indication of K. I told the CA to stop because I couldn't see K and I thought that was the grass directly in front of us. He stopped immediately and we were trying to find indications of the apron; the taxiway and the edge of the grass. He pointed out to me that there were what appeared as tire marks directly in front of us but again we were unsure so the CA opened his window completely (took it off the hinge) to get a better view. It became clear when we saw another blue taxi light abeam his window that we were facing the grass. At that point we had discussed if we were still on the edge of the apron or on the grass and neither of us could tell since there was no clear definition between the two. We never felt a drop off either. He asked me to call ops so that they could come out and possibly push us back and at least check if we were still on concrete so that we can continue the turn or determine if we needed maintenance. On a side note while waiting we heard another airplane discuss with ground the poor conditions on the ground and ground offered a follow me car. Ops would not answer the radio so I believe he asked ground if they could contact our ops so that they could come out to us. While waiting we had shut down engine #1 and shortly after we shut down engine #2 when the plow started clearing the taxiways and the apron. The conditions started changing quickly and daylight combined with better visibility and plowed taxiways made it clear to us that we were facing grass. I would say more than 30 minutes had passed without any word from ops and at least 45 minutes for them to actually come out to our location. Ops confirmed that our nose wheel was on the grass and not the concrete. We both discussed that we could no longer simply get pushed back and go and that we needed a maintenance inspection even though we were sure there was no damage. We coordinated with ops; dispatch; on call chief pilot; airport operations; customs and our flight attendant. The CA made multiple announcements to the passengers. Our flight attendant did an amazing job at keeping everyone happy on board considering our situation. We knew we would have to deplane and being in Canada didn't make it any easier. We were told it would take hours to get a bus to unload the passengers. Airport operations brought airport vehicles and we eventually deplaned our passengers 4 at the time. After everyone deplaned I walked outside and saw that our nose wheel was 3-4 feet beyond the apron and onto the grass. Eventually a tug was hooked up and we were pushed back to the gate.The biggest threat was the weather and the conditions at the airport that early morning along with our failure to have exact situational awareness as to our precise location on the ground. We never realized how far back we had been pushed back and our angle to taxiway K. The threat of having both our side windows frozen also compounded the situation. The threat of taxiway K and apron not being plowed hiding taxiway edges. I think there is a lot to be learned for me from all of the events that took place that day. I think we could have had better communication with our ops people while we were getting pushed back as to the location of taxiway K. In these conditions I realized how important it is to have our side windows clear in order to have a better view of our surroundings. I think the possibility of using a follow me car could have also prevented the situation. Maybe better communication with ground. Simply asking if a left turn out was possible could have prevented our situation. In my opinion having had taxiways and aprons plowed would have made all the difference since we would have been able to distinguish our surroundings better. Another tool that could have prevented our situation would be technology. GPS tracking for taxiing such as iPads could have helped us realize our exact location at all times. Even during these events I was thankful that it took place with the crew I had. I believe the CA and I always had great CRM and we really tried to work well together to accomplish the flight safely. I know that our nose wheel was on the grass but I am glad that we stopped when we did and not later. I wish I had seen that blue taxi light 4 feet earlier as that would have prevented this whole thing. I'm glad we started both engines before moving so that my work load was focused on looking outside as opposed to starting engines or doing other things. This goes to show the importance of being vigilant at all times along with having great CRM in the cockpit. Air Carrier flight crew describes the events leading up to a taxiway excursion while attempting to taxi away from the gate with new snow covering all surfaces. The aircraft is eventually towed back to the gate for a maintenance inspection.